This invention relates to an improvement in a solid state laser which is pumped by a diode laser (semiconductor laser).
Typical of diode laser pumped solid state lasers known in the art is an Nd:YAG (Neodymium Doped Yttrium Aluminum Garnet) laser. The diode laser pumped Nd:YAG lasers are generally classified into two types, i.e., a side pumped type laser and an end pumped type laser as disclosed in U.S. Pat. Nos. 4,575,854 and 3,982,201, respectively. A side pumped type laser has a diode laser array to for illuminating the side of an Nd:YAG laser rod thereby supplying pumping power to the laser rod, while an end pumped type laser introduces light from a diode laser into the end of an Nd:YAG laser rod for supplying the latter with pumping power. The end pumped type laser is advantageous over the side pumped type laser because it allows the laser rod to absorb the pumping light efficiently and has a high lasing efficiency.
A problem with the end pumped type laser, however, is that the pumping light which can be incident into the laser rod is limited. Specifically, since the pumping light can be introduced into the laser rod only at the opposite ends of the laser rod where a pair of resonance mirrors are disposed, the number of diode laser usable for pumping purpose is limited. It follows that the output power of Nd:YAG laser cannot be increased unless the output of the individual diode laser is increased. For this reason, an increase in the laser output power is difficult to achieve.